The Mother Sea Whelk only appears in the episode, "Whelk Attack," when she was raising her whelk kids as her leader. She appeared to be big as a giant just like her kids. She can inhale and use her long tongue to eat everything and everybody. She can also exhale purple bubbles/goop.
The Mother Sea Whelk is a very large snail with a light orange spiky shell and light purple skin. Her children are often seen with her with the same appearance but smaller. She has yellowish-white pointy teeth as well.